Antihistamines
What are Antihistamines?
Antihistamines are drugs used to treat symptoms of allergies. They counteract the effects of histamine, a chemical produced by the immune system during allergic reactions.
Concepts:
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Allergies: Allergies occur when the immune system overreacts to substances (allergens) that are typically harmless. Common allergens include food, dust, pollen, pet dander, mold, insect bites, latex, and certain medications.
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Histamine: Histamine plays a role in various bodily processes, including inflammation, gastric acid secretion, and transmitting messages between nerve cells. When the body encounters an allergen, histamine is released, causing allergy symptoms.
Types of Antihistamines (H-1 and H-2)
Antihistamines are medications that block the effects of histamine. They are divided into two major subtypes:
- H-1 blockers: Used to treat allergy symptoms.
- H-2 blockers: Used for gastrointestinal conditions like acid reflux and ulcers.
The H-1 blocker subtype is further broken down into two groups โ first-generation antihistamines and second-generation antihistamines.
First vs. Second Generation Antihistamines (H-1)
- First-generation antihistamines: Older and can cause drowsiness as they cross the blood-brain barrier.
- Second-generation antihistamines: Newer, cause less drowsiness, and are considered safer.
Examples of Antihistamines:
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First-generation H-1 blockers:
- Brompheniramine (Childrenโs Dimetapp Coldยฎ).
- Chlorphenamine (Chlor-Trimetonยฎ).
- Clemastineย (Dayhistยฎ).
- Cyproheptadineย (Periactinยฎ).
- Dexchlorpheniramineย Dimenhydrinateย (Dramamineยฎ).
- Diphenhydramineย (Benadrylยฎ).
- Doxylamineย (Vicks NyQuilยฎ, Tylenol Cold and Couth Nighttimeยฎ).
- Hydroxyzineย (Vistarilยฎ).
- Phenindamineย (Nolahistยฎ).
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Second-generation H-1 blockers:
- Azelastineย (Astelinยฎ).
- Loratadineย (Claritinยฎ).
- Cetirizineย (Zyrtecยฎ).
- Desloratadineย (Clarinexยฎ).
- Fexofenadineย (Allegraยฎ).
- Levocetirizine (Xyzalยฎ). <-----
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H-2 antihistamines include:
- Cimetidineย (Tagamet HBยฎ).
- Famotidineย (Pepcidยฎ).
- Nizatidineย (Axidยฎ).
- Ranitidineย (Zantacยฎ). <------
Uses:
Besides allergies, antihistamines treat conditions like colds, food allergies, motion sickness, anxiety, heartburn, ulcers, and more. In relation with Long COVID, it is used to treat ๐ Research ๐งช/๐คข Main Diseases (Notes)/Mast Cell Activation Syndrome (MCAS)
Side Effects:
- H-1 blockers:
- First-generation: Drowsiness, dry mouth, blurred vision, dizziness, low blood pressure, rapid heart rate, etc.
- Second-generation: Headache, cough, tiredness, sore throat, abdominal pain, nausea.
- H-2 blockers: Drowsiness, joint pain, headache, dizziness, etc.
It's essential to consult with a healthcare provider to determine the best antihistamine for individual needs. Some antihistamines may not be suitable during pregnancy or breastfeeding.
Long-term use of certain antihistamines might increase the risk of Dementia.
Dosage Forms:
Antihistamines are available in various forms, including liquids, lotions, syrups, tablets, nasal sprays, creams, capsules, and more.
Conclusion:
While histamine plays a protective role in the body, it can sometimes overreact, leading to allergic symptoms. Antihistamines can help manage these symptoms. Always consult with a healthcare provider before starting or changing medication.